Query regarding CST

1) Mumbai will buy goods from tamilnadu - issue form C - Ask for E-1 form from Tamilnadu seller, 

2) Mumbai will enroute the goods in transit to kerala, without charge of any value addition or additioal CST, - kerala party will issue form C to mumbai 

3) be careful that nowhere in documents from tamilnadu the kerala party has to be mentioned, but it would get endorsed by mumbai party only on transport documents alongwith their invoices. i.e tamilnadu party and kerala party dont know each other upto consignment of goods, but mumbai party endorse the documents in favor of kerala party. 

Thank you Sir

Please Guide me .........

Our client is situated in Mumbai. He wants to buy goods from our company but our company is ragistered in delhi we want to sell those in Mumbai. so wat should i do for client and company?.

So how the billing is to be done.........?